1.5-μm band polarization entangled photon-pair source with variable Bell states

Area of Science:

• Quantum Optics
• Photonics
• Quantum Information Science

Background:

• Generating entangled photon pairs is crucial for quantum communication and computation.
• Existing sources often lack the flexibility to produce arbitrary entangled states or operate efficiently at telecommunication wavelengths.

Purpose of the Study:

• To develop and characterize a polarization-entangled photon-pair source capable of generating arbitrary entangled states.
• To demonstrate the source's performance using quantum state tomography and Bell inequality tests.

Main Methods:

• Utilized cascaded optical second nonlinearities (second-harmonic generation and spontaneous parametric down-conversion) in a periodically poled lithium niobate (PPLN) ridge-waveguide device.
• Employed an optical phase bias compensator (OPBC) in a Sagnac loop interferometer and a half-wave plate for Bell state exchange.
• Performed experiments including two-photon interference, quantum state tomography, and Clauser-Horne-Shimony-Holt (CHSH) inequality violation tests.

Main Results:

• Achieved high experimental visibilities (96%) and fidelities (97%) for generated entangled states.
• Demonstrated a violation of the CHSH inequality with an S parameter of 2.71.
• Observed stable performance with high coincidence counts (approx. 170 counts/sec) during Bell state exchange.
• Confirmed quantum states align with the Werner state model based on photon-pair generation rates.

Conclusions:

• The developed PPLN-based photon-pair source reliably generates arbitrary entangled states in the 1.5-μm band.
• The source exhibits excellent performance metrics, suitable for advanced quantum information processing and communication.
• The ability to exchange between Bell states without performance degradation highlights its practical utility.